Apparatus for making fiber optical image transfer devices



March 12, 1968 R. F. WOODCOCK APPARATUS FOR MAKING FIBER OPTICAL IMAGETRANSFER DEVICES 4 Sheets-Sheet 1 Original Filed Nov. 23, 1960 I NVEVTOR. R/CHAHD F WOODCIOC K March 12, 1968 R. F. WOODCOCK 3,

APPARATUS FOR MAKING FIBER OPTICAL IMAGE TRANSFER DEVICES Original FiledNov. 23, 1960 4 Sheets-Sheet 2 F/G. 5. l i

lNVEA "FOR. RICHARD E WOODCOCK March 12, 1968 APPARATUS F R. F. WOODCOCKI 3,373,006

OR MAKING FIBER OPTICAL IMAGE TRANSFER DEVICES Original Filed Nov. 23,1960 4 Sheets-Sheet 3- March 12, 1968 R. F. WOODCOCK APPARATUS FORMAKING FIBER OPTICAL IMAGE TRANSFER DEVICES 4 Sheets-Sheet 4 OriginalFiled Nov. 23, 1960 FIG. 2/.

1 9 7 6 5 y v H 0 a NH 9/ F/& /8. 36

INVENTOR. RICHARD E WOODCOCK United States Patent Office 3 Claims. (Cl.65-1) ABSTRACT OF THE DISCLOSURE Supporting means of refractory materialfor compacting and fusing a length of bundled glass clad fibers. Thesupporting means has a bottom member, a cover memher, side walls andopposite open ends forming a channel in which the bundle may be placedfor compaction and fusion. Facing sides of the bottom and cover membershave oppositely disposed portions of their lengths sloped gradually awayfrom each other in directions from points internally of the channeltoward each of its opposite open ends. At least one of the members ismovable toward the other for compressing the length of bundled fibers toa greatest amount intermediately of its extension and in progressivelylesser amounts away therefrom.

This invention relates to improvements in fiber optical image transferdevices and has particular reference to a novel means of fabricatingdevices of the type embodying a great number of relatively smallelongated light-conducting fibers or filaments including multifiberswhich are arranged in side-by-side relation with each other and whichhave at least their ends intimately bundled together to provide compactlight-emitting areas or faces at the extremities thereof.

This application is a division of applicants copending application Ser.No. 71,872 filed on Nov. 23, 1960, now Patent No. 3,215,029 issued Nov.2, 1965, which copending application comprises a continuation-impart ofapplicants earlier copending application Ser. No. 826,762, which earlierapplication was filed on July 13, 1959 and is now abandoned.

In devices of the above character wherein a considerable number ofelongated, relatively fine fibers or multifibers of light-conductingmaterial are bundled together and used collectively to transmit light oroptical images from one location to another, it is of great importance,particularly in the transferring of optical images, that the ends of thefibers at each of the light-accepting and emitting faces of the devicesare substantially identically geometrically arranged or patterned. Whensuch devices are used as diagnostic instruments such as gastroscopes orendoscopes or the like, their cross-sectional size must be kept to aminimum while at the same time being capable of transferring a maximumamount of image-forming light with a high degree of accuracy andresolution.

Further, where the image transfer devices are adapted to serve asfaceplates and the like for vacuum tubes or for other sealed tubes, itis of first importance that the fibers or multifibers in the devices bejoined together in intimate, vacuum-tight relation.

While multiple fiber, image-transfer devices, including devices knowngenerally as fiberscopes and fiber optical faceplates, have been madeand used heretofore, their optical efiiciencies, particularly those ofresolution, contrast and definition have not been as good as might bedesired. In this regard, it has been found that these inefiiciencies areprimarily due to lack of compactness and 3,373,006 Patented Mar. 12,1968 similarity of geometrical configuration of the fibers at theopposite ends of the devices and to inferior optical finishes at thelight-accepting and emitting faces thereof.

In addition, fiber optical faceplates of any substantial size have beendifiicult to form in that fusing of the fibers in such faceplates intovacuum-tight relation has frequently resulted in the entrapment of airbubbles and the like between the fibers, such bubbles tending to extendinto the centers of fibers for blocking light transmission therethrough.

The accuracy with which images may be transferred by a device of theabove character is dependent upon the degree of similarity between thegeometrical patterns of the ends of the fibers at the light-acceptingand light-emitting faces of the device whereas the degree of resolutionwith which images are transferred is dependent upon the cross-sectionalsize of the fibers and the compactness with which they are grouped atsaid light-accepting and emitting faces. The smaller fibers and morecompact groupings thereof produce the best resolution, within practicallimits of fiber sizes. As for the intensity or amount of light which canbe transferred through a device of the above character, the quality ofthe optical finish on the light-accepting and light-emitting faces ofthe device is of prime importance. High quality optical finishes on theend faces of such devices overcome the efiects of diffusion which wouldexist at a poorly polished surface and thus allow more light to enterand pass through the fibers thereby improving the contrast anddefinition of the transferred images.

The present invention provides novel means for manufacturing superiorfiber optical image transfer devices which are adapted to overcome theabove-mentioned inefficiencies common to conventional devices of asimilar nature and, accordingly, it is an object of the presentinvention to provide an improved fiber optical image transfer devicehaving exceptionally high efiiciency in image resolving power andaccuracy of image reproduction and method and apparatus for making thesame.

Another object is to provide an improved means and method for assemblingan elongated array of relatively fine light-conducting fibers orfilaments in fixed, accurate, side-by-side aligned relation with eachother with the cross-sectional pattern of at least the opposite ends ofsaid array of fibers being accurately identically geometricallypatterned.

Another object is to provide an improved apparatus for manufacturingfiberscopes, more particularly of the flexible type wherein thelight-conductin fibers thereof are intimately bundled and securedtogether only throughout a predetermined section at each of theiropposite ends while being disconnected and free to flex individuallybetween said opposite ends.

Another object is to provide novel means for forming the end sections ofa flexible fiberscope of the above type wherein the light-conducting andsimultaneously fused together at their opposite ends in such manner asto reduce the cross'sectional size of the end sections of thefiberscopes to a minimum without reducing the cross-sectional sizes ofthe individual fibers or, in any way, deterring the light-conductingcapabilities of said fibers.

A further object is to provide a flexible fiberscope of the abovecharacter having the exposed opposite ends of the fibers thereofsubstantially identically geometrically patterned and so interfitted infused relation with each other as to collectively form a substantiallyuninterrupted or continuous face portion at each end of the fiberscope.

Another object is to provide a flexible fiberscope device of the abovecharacter which is adapted to be subjected to elevated temperaturesbelow the annealing point of the glass thereof when in use.

fibers thereof are compacted A further object is to provide an improvedapparatus for manufacturing fiber optical faceplates having the exposedopposite ends of the faceplate fibers arranged in substantiallyidentical geometrical patterns and having the fibers fused together inintimate, vacuum-tight relation throughout their length.

Another object of this invention is to provide such an apparatus formanufacturing fiber optical faceplates which are of substantial sizeincluding faceplates which may be relatively narrow for their length.

A still further object is to provide a simple, reliable, efficient andinexpensive apparatus for fabricating fiber optical devices of the abovetype which may be provided at the opposite ends thereof with highlyfinished optical surfaces, the device in general having high opticalefficiencies and accuracy of image reproduction with excep- 'tionalimage resolving powers.

Other objects and advantages of the invention will become apparent fromthe following description when taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a diagrammatic illustration of a part of the apparatus used informing certain of the fiber optical devices of this invention;

FIG. 2 is a perspective view of the mandrel or drum shown in FIG. 1 uponwhich has been Wound a thread or filament of light-conducting materialfor use in forming said devices;

FIG. 3 is a perspective view of a helix or hoop formed of said filamentwhich has been removed from the mandrel of FIGS. 1 and 2;

FIG. 4 is a side cross-sectional view of a combined holder and formingmember in which an assembly of fibers such as the plurality of hoopsillustrated by FIG. 3 have been placed for subsequent processing;

FIG. 5 is a front cross-sectional view of said forming member and meansused to fuse the fibers or filaments of a section of the assembly ofhoops as shown in FIG. 4;

FIG. 6 is an enlarged fragmentary cross-sectional view of the formingmeans and fibers illustrating a first stage in the forming of the fusedend sections of a fiberscope;

FIG. 7 is an enlarged view generally similar to FIG. 6 illustrating alater stage in the forming of said fused fiber section;

FIG. 8 is an enlarged fragmentary side elevational view of an assemblyof fiber hoops having a fused section which is illustrateddiagrammatically as being transversely severed in accordance with afurther step in the invention;

FIG. 9 is a fragmentary plan view of the assembly of fiber hoopsfollowing the operation illustrated by FIG. 8;

FIG. 10 is a partial cross-sectioned view of an optical instrumentembodying a fiber optical fiberscope device of the character describedabove;

FIGS. 11 and 12 are enlarged views generally similar I to FIGS. 6 and 7each illustrating a different stage in an alternative method of forminga fused section in an assembly of fiber hoops;

FIG. 13 is an end view of a fiber optical device which was initiallyformed by the alternative method illustrated in FIGS. 11 and 12;

FIG. 14 is a perspective view of a mandrel such as is shown in FIG. 2upon which has been wound a thread or filament of light-conductingmaterial, the thread forming a helix to be used in preparing fiberoptical faceplates;

FIG. 15 is a plan view of a fiber ribbon cut from the helix shown inFIG. 14;

FIG. 16 is a side cross-sectional view of a holder used for assemblingthe fiber ribbons of FIG. 15 to form a fiber optical faceplate;

FIG. 17 is a side cross-Section view similar to FIG. 16 showingmultifibers assembled in a holder to form a fiber optical faceplate;

FIG. 18 is a partial front cross-section view similar to FIG. 5illustrating said holder and means used to fuse the fiber ribbons ormultifibers into vacuumtight relation;

FIG. 19 is a partial side cross-section view similar to FIG. 4illustrating a subsequent step in the formation of such fiber opticalfaceplates;

FIG. 20 is a front elevation view of a fiber optical faceplate preparedby this invention; and

FIG. 21 is an end elevation view of the faceplate illustrated in FIG.20.

As mentioned hereinabove, the fiber optical device of the invention iscomposed of a considerable number of elongated relatively finelight-conducting filaments or fibers each of which must be capable ofreadily and efficiently transferring light from one of its ends to theother thereof. In a preferred form of this invention, the fibers embodya core part of a relatively high index glass such as, for example, anoptical flint glass having an index of refraction of approximately 1.62and a relatively thin outer coating or cladding of a low index glasshaving substantially the same coefficient of expansion and meltingtemperature as the high index core glass. An optical crown or soda-limeglass having an index of refraction of approximately 1.52, for example,might be used. It is to be understood, however, that the fibers may beformed of combinations of other types and indices of glasses or othersuitable materials and also that uncoated fibers could be used to formthe devices of the invention. In most instances, coated or clad fibersare preferred since the low index outer cladding will optically functionin a well-known manner to insulate one fiber from an adjacent fiber in abundle thereof by insuring total internal refiection of all lightentering a fiber at one end and travelling therethrough to its oppositeend.

By referring more particularly to the drawings, it will be seen that inFIG. 1 there is shown diagrammatically means for forming a continuouslight-conducting fiber 20 of the above-described clad type. The formingof the fiber 20 is accomplished by initially providing a rod 21 of highindex core glass having a sleeve 22 or outer surrounding layer of lowindex cladding glass and placing one end of the rod and sleeve assemblywithin a ring-like heating element 23 (of known construction) to softenthe glasses of the assembly sufiiciently to permit a uniform endwisedrawing of the fiber 20 from the rod and sleeve assembly. The size ofthe fiber 20 is controlled by the rate of uniform drawing when the rod21 and sleeve 22 assembly is heated to a proper drawing temperature. Itis pointed out that regardless of the fineness or size to which thefiber is drawn, the relative proportions of the cross-sectional sizes ofthe core and cladding parts of the fiber 20 will remain substantiallythe same as that of the rod 21 and sleeve 22 assembly. Thus, therelative cross-sectional sizes of the rod 21 and sleeve 22 are initiallycontrolled in known manner in accordance with the relative proportionsdesired of the parts of the finally formed fibers 20.

Having thus provided means for forming a continuous optically insulatedfiber 2i accurately constructed helices or hoops 24 of the fiber 20,such as shown in FIG. 3, can be wound directly on a drum or mandrel 25which, in the arrangement shown, functions to draw the fiber 20 to adesired size While simultaneously providing means to support theconvolutes of the helices 24.

The fiber 20 is directed around an idling roller 26, over a guide member27 and through a transverse U-shaped groove 28 in said guide member andthe leading end of the fiber 20 is taped or otherwise anchored to themandrel 25. The mandrel which is preferably carried on the spindle of amachine lathe or the like (not shown) is rotated at a precontrolleduniform rate to draw the fiber 20 and simultaneously produce successiveconvolutes or turns thereof about its outer peripheral surface. In orderto accurately form or wind a substantially closed helix 24 on themandrel 25, the guide member 27 is preferably suitably mounted on andcarried by a conventional lathe carriage traversing mechanism or thelike (not shown) so as to be driven in a direction parallel to the axisof rotation of the mandrel at a precontrolled rate in accordance withthe rate of rotation of the mandrel.

The fiber helices 24 formed on the mandrel 25 can be used for formingfiber optical image transfer devices of the fiberscope or faceplatetype. Where the helices are to be used in forming fiberscopes, theoverall length of the fiber optical image transfer devices of theinvention will be substantially equal to the circumference of themandrel 25 as will become more readily apparent from the description tofollow. Therefore, the size or diameter of the mandrel is chosen inaccordance with the length desired of the device to be manufacturedwhile at the same time, the thinness of the fiber 20 and diameter of themandrel 25 are selected to be such as to avoid breakage of the fiber bytoo sharp a bend for the particular size fiber being wound.

Due to the fact that use of the helix for forming a fiberscope requiresthat the helix or hoop 24 be removed from the mandrel 25 to provideindependent structures such as shown in FIG. 3, the mandrel 25 isprovided with a removable section 29 having an outer surface 30 shapedto the outer peripheral surface curvature of the mandrel to form asmooth continuous winding surface completely around the drum when thesection 29 is in place as shown in FIGS. 1 and 2. The section 29 isremoved by sliding the same endwise out of its receiving channel 31 inthe mandrel and the section 29 and channel 31 are preferably taperedtoward one end of the mandrel to interfit with each other and cause thesection 29 to drop down or away from the helix 24 when slid endwise outof its receiving channel. With the helix 24 loosened on the drum byremoval of the section 29, it can be easily and simply slipped endwiseoff the mandrel.

It should be understood that other types of winding drums or mandrelswhich may be collapsed in a wellknown manner might also be used to formhelices 24 to be used in forming fiberscopes. It is only of importanceto this embodiment of the invention that means is provided forpermitting the helices 24 to be easily removed from the winding drum ormandrel 25 without disrupting the above-mentioned closely woundrelationship of the convolutes of the helices.

Prior to the removal of the helices 24 from the mandrel 25, however,means must be provided to keep the convolutes of the helices 24 in fixedrelation to each other and to render the helices 24 self-supporting whenremoved from the mandrel. This is accomplished by cementing theconvolutes of the helices 24 together along a transverse section orstrip 32, such as shown in FIG. 2. It has been found that a cementformed of cellulose nitrate in a solvent of nitromethane will provide avery satisfactory bond and that the cellulose nitrate will burn off veryreadily leaving substantially no residue when the fibers 20 of thehelices 24 are heated to fusing temperatures in the steps of the processto follow. Such a cement or others having similar characteristics willpermit a clean and secure fusion between the adjoining parts of thefibers.

Previous to the winding of a helix 24 on the mandrel 25, the windingsurface of the mandrel may be covered with a plastic sheet material toprevent the cement from sticking to the mandrel and hindering theremoval of the helix.

In assembling the fiberscope device of the invention, a plurality ofhelices or hoops 24 each of a width substantially equal to that desiredof the device are first stacked in progressive surrounding relation witheach other to form a bundle of a thickness slightly greater than thatdesired of the finished device.

It is pointed out at this time that the helices or hoops 24 may beformed individually or one at a time on the mandrel 25 to substantiallythe width desired of the finished device or a wide helix may be formedacross the entire width of the mandrel, provided with a cemented strip32 and thereafter cut up into a plurality of more narrow helices orhoops by severing the strip 32 in the direction of the convolutes.

During the stacking of the hoops 24, it is important that all the layersof the resultant bundle thereof have the same helix direction. That is,each hoop 24 must be progressively placed in surrounding relation withthe previous hoop and the direction of wind or helix of each hoop shouldmatch that of its predecessor.

While only single layer helices or hoops 24 have been described above,it should be understood that multi-layer hoops may be formed on themandrel 25 particularly in instances where very small diameter fibersare used. In such instances, each successive layer would preferably bewound separately over its preceding layer in the same helix directionand the successive layers would be joined together with a strip ofcement such as described above.

Since, in the present invention, a predetermined section of the stackedor bundled hoops 24 is to be fused together with heat and pressure toform. the opposite ends of the final fiber optical device as will bedescribed in detail hereinafter, the assembly of hoops 24 is madedirectly in a support 33 constructed of a refractory material preferablyof the type disclosed in patents No. 2,440,187 and No. 2,764,491. Therefractory material disclosed in said patents is exceptionallygeometrically stable and distortionless when subjected to glassfusingtemperatures and molten glass will not adhere to its surfaces by fusion.However, to facilitate removal of the fused assembly of hoops, a partingagent or gold foil or the like (not shown) may be used between the fiberbundle and refractory material to avoid possible difiiculty in removingthe glass of the fibers from the support 33 which difiiculty mightresult from glass flowing into scratches or other imperfections in thesupport 33. The support 33 (see FIGS. 4 and 5) is provided with arectangular U-shaped channel 34 extending from front to back and openingoutwardly at the top thereof. Where gold foil or the like is not used tofacilitate ultimate removal of the fiber hoop section from the support,the bottom and side walls of the channel 34 can be lined with removablerectangular fillers or blocks 35 and 36 respectively, also of saidrefractory material, between which, as shown, there is provided a spaceof a width substantially equal to the width desired of the fiber opticaldevice to be formed.

The hoops 24 being of a width substantially equal to that of the spacebetween blocks 36 automatically become superimposed with each other whenstacked in the support 33. That is, as shown in FIGS. 4, 5 and 6, thefibers in the hoops stack in regular aligned rows without tending tonest between fibers of adjacent hoops. It will be noted, however, thatdue to the cross-sectional shape of the fibers 20, which are circular asis most generally the case, there are a great many voids or spacesbetween the adjacent fibers even though the fibers are relativelytightly packed or in adjoining side-by-side relation with each other asshown in FIG. 6.

While the fibers 29 may be cemented or otherwise secured together inthis condition to form a flexible fiberscope as has been doneheretofore, it can be seen that the cross-sectional area of the bundlewhich includes the voids or spaces between the fibers would not providea light-receiving or emitting face capable of producing the best imageresolution.

The present invention provides for the compacting of the fibersthroughout the section of the bundle in support 33 while simultaneouslyfusing the same together thereby reducing the overall cross-sectionalsize of the bundle and eliminating the voids or spaces between thefibers while preventing the entrapment of air bubbles and the likebetween the fibers.

To this end, a cover member 37 is provided to fit over the support 33and embodies a rectangular depending section 38 which fits intimatelyinto the space between the blocks 36 and engages the top layer of fibersof the stacked bundle thereof. The cover member is preferably formed ofthe same refractory material as that of the support 33 and is providedwith side parts 39 adapted to fit aaginst the outer sides of the support33 and accurately guide 7 the cover member 37 downwardly during thecompacting and fusing of the fibers 20.

In performing the fusing operation, at which time the fibers 20 arecompacted, the support 33 and cover 37 with the stacked hoops 24 thereinare surrounded with a heating element 40, such as shown in FIG. 5, andthe assembly is placed between the base 41 and plunger 42 of a suitablepress. The heating element 40 may consist of conventional resistanceheating coils or a strip or band of durable high resistance metal suchas Nichrome which when having its ends 40a and 40b connected across asuitable supply of electrical current will heat the glass of the fibersin the support 33 to a fusing temperature. However, the heating element40 is dis-posed around the refractory members 33 and 37 in contacttherewith to provide for heating of the entire periphery of the sectionof the hoops 24 to be fused, the heating element be ing adapted toremain in contact with the refractory members during relative movementof the members. Thermocouples (not shown) may be placed near the sectionof the fibers to be fused and electrically connected in circuit with theelement 4t) for use in controlling the heat produced thereby in aconventional manner.

As will be readily understood, the support 33 and the cover 37 arearranged between a base 41 and a plunger 42 by means of which the coverand support can be forced together for comp-acting the hoop sectionswithin the support 33 to remove voids and spaces from between the hoopfibers. Since it is desirable to contain a large part of the heatdevceloped by the element 40 within the area of the fibers to be fused,a heat-insulating layer of conventional insulating brick or millboard 43or the like is provided around the assembly of the heater 40, support 33and cover 37, see FIG. 5, for insulating the heating element 40 from thebase 41 and from the plunger 42. However, the sides of the refractorymembers '33 and 37 which are not contacted by the heating element 40 arepermitted to remain uninsulated for a purpose which will be explainedbelow. In order to further insulate the base 41 and plunger 42 from theheat of the element 40, while still permitting the same to make a solidengagement With the respective support 33 and cover part 37, stainlesssteel plates 44, electrically insulated from the heating element 40 bysheets of mica or the like 45, are placed against the respective supportand cover parts 33 and 37 and tubular extensions 46 and 47 of rigidheat-resistive refractory material extend through the insulating brickto span the space between the steel plates and the respective base andplunger parts of the press. The plates 44 distribute the load on support33 and cover 37 uniformly to avoid cracking thereof. The force of theplunger 42 is exerted through the tubular extensions 46 and 47 which actto support the weight of the fusing apparatus and the pressure appliedthereto without compressing the insulation 43.

In performing the fusing and compacting of the fibers 20 throughout themajor portion of the section of the bundle of fibers which is within thesupport 33, a controlled squeezing pressure is applied to the fiberbundle by forcing the cover member 37 downwardly with the plunger 42while heating the fibers 20 to a temperature which is sufficient to fusethe claddings thereof together. This causes the fibers to be compressedand simultaneously deformed only an amount suficient to close off orfill in substantially all voids between the fibers without causing amaterial reduction in the cross-sectional area of the fibers. That is,for example, fibers 2t) which are round in cross-section will bedeformed into rectangular cross-sectional shape without substantiallyaltering the cross-sectional area of the fiber. For example, with fibershaving a core part of 1.62 index fiint glass and claddings of 1.52 indexsoda-lime or crown glass, compacting of the fibers at fusingtemperatures of from 1140 F. to ll50 F. maximum for a period of time ofapproximately ten minutes at a pressure of approximately 200 lbs./ sq.inch maximum will produce good 8 results, it being understood that thepressures, temperatures and time cycles will vary in accordance with thetype of glasses or materials used to form the fibers 20.

In referring more particularly to FIG. 4, it will be seen that thefiller or block 35 and the depending part 38 of the cover 37 can bebevelled at 35a and 38a respectively so as to gradually slope away fromeach other adjacent opposite ends of the opening in which the fiberhoops 24 are supported. The bevels 35a and 38a function to provide apressure gradient on the fibers 20 of the hoops 24 wherein, during theabove-mentioned fusing operation, the compressing or compacting force onthe bundle of hoops 24 is at a maximum along a plane extendingtransversely through the center of the hoop section to be fused and isof a gradually lessening degree extending in an outward direction alongthe length of said fibers toward respective opposite bevels 35a and 38a.

Alternatively or in addition to the described pressure gradient, atemperature gradient can be provided in the hoop section to be fusedwherein the temperature during a fusing operation is greatest in a planeextending through the centermost part of the section of fibers beingfused. This temperature gradient in the illustrated embodiment of theinvention results from positioning of the heating element 40 in a ringaround the hoop section to be fused and from positioning of theinsulation 43 in a ring around the heating element while leaving thesides of the refractory members 33 and 37 uninsulated as describedabove. As will be readily understood, the thickness of the insulation 43and the overhang of the insulation 43 at the side of the heating element40 can be proportioned relative to the heat developed by the heaterelement and to the areas of the refractory members which are free toradiate heat without obstruction to achieve the desired temperaturegradient wherein the center portions of each fiber can be heated to arelatively high fusing temperature and portions of the fibers extendingprogressively outward from said center portions can be heated torelatively lower fusing temperatures. Although a ring-shaped, resistancetype of heater element is herein described for purpose of establishing atemperature gradient in the section to be fused, other similar heatingelement arrangements utilizing dielectric heating devices for examplefor achieving said temperature gradient are within the scopeof thisinvention. The combination of the described pressure and temperaturegradients causes the centermost area of the section of fibers 2t: withinthe support 33 to soften and fuse before the outer areas thereof whichfor example, are adjacent the bevels 35a and 38a. In cases wherecomplete fusion is desired, this effect gradually forces air or gasesoutwardly from between the fibers being fused and produces asubstantially perfect air-tight fusion between the fibers withoutentrapment of air or gas bubbles or the like in the fused areas.

It will be noted that although the described temperature gradient is tobe desired, close control of the temperature in the fiber section to befused is required and it is desirable to prevent the development of hotspots within the section to be fused. This prevents the development ofharmful flow patterns within the fibers to be fused and assuresretention of the identity of individual fibers and fiber coatings bypreventing excessive melting of the fiber materials. For this purpose,the heater element 40 is disposed in contact with the refractory members33 and 37, the heater element being adapted to move With the refractorymembers during compression of the fiber section to be fused. Thisconstruction assures rapid response of the heater element controls tochange of temperature within the fiber section being fused and assuresconstant heating effectin response to a constant current supply to theheater element. For further control of the heating process to preventthe development of hot spots in the fiber section, the insulation 43 canbe shielded with aluminum foil or can be adapted by other suitableradiation-shielding means ii for decreasing heat-dissipating radiationat localized areas of the insulation, thereby to assure that the fibersection Will be properly heated without random temperature gradientstherein other than the desired temperature gradient above described.

In FIG. 7, which illustates a cross-section of the fiber bundle afterbeing fused and compressed, it can be seen that the fibers 24 areretained in precisely the same geometrical or accurately superimposedrelation with each other as they were before fusion (see FIG. 6). Thefibers 20, however, have been reformed to a substantially rectangularcross-sectional shape by being forced downwardly against the block 35.

After fusing and cooling of the section of the fiber hoops 24 which arestacked in the support 33, the cover 37 is removed and the fused fiberbundle is lifted out of the support 33, preferably by sliding the blocks35 and 36 along with the fiber bundle out of the channel 34. Uponremoval from the channel 34, the blocks 35 and 36 may be easily liftedfrom the fiber bundle.

While, as stated above, glass will not stick to the refractory materialdisclosed by Patents No. 2,440,187 and No. 2,764,491, it is preferableto use at least the filler blocks 35 in the construction of the support33 since slight scratches or other imperfections on the interfacebetween the refractory material and the glass of the fibers resultingfrom continued use of the support 33 might permit some glass to flowthereinto during the fusing operation. The filler block 36 can also beused if desired but is not entirely necessary. If such blocks are notused and if glass should fill scratches and the like in the support 33,difiiculty might be experienced in removing the finally fused fiberbundle from the support if it were constructed as a one-piece unit. Withthe construction shown and described above, the adjoining surfaces ofthe blocks 35, 36 and the channel 34 will always be free to sliderelative to each other and permit quick and easy removal of the fiberbundle.

After removal from the support 33, the fused section of the fiber bundleis placed substantially centrally over a support 43 having a groove 49therein. FIG. 8, with the helix direction of the fibers 2! in the bundlealigned substantially at right angles to the groove 49. The fusedsection is then severed in a direction along the axis of the groove 49as illustrated in FIG. 8. A suitable diamond impregnated saw or otherthin cutting tool of known construction is used to sever the fiberbundle.

When opened up, as shown in FIG. 9, the once continuous fiber bundle ofstacked fiber hoops 24 become an elongated fiberscope with substantiallyidentical opposite end faces 51 and 52. Due to the fact that the ends 51and 52 were once integral and the amount of stock removed from betweenthe same is only equal to the thickness of a saw cut, the geometricalpatterns of the fibers at the faces 51 and 52 are substantiallyidentical. Furthermore, since the individual helices or hoops were eachinitially formed to have substantially equal outside diameters and werestacked in progressive surrounding relation with each other (see FIG.4), the saw cut illustrated in FIG. 8 will sever each of the fibers 29in a plane substantially normal to their longitudinal axes and therebycause all of the fibers 20 of the severed assembly to be ofsubstantially the same length.

The end faces 51 and 52 of the device shown in FIG. 9 are opticallyground and polished, with the use of conventional equipment commonlyused for forming optical flats thereby rendering the device ready foruse as a fiberscope. In FIG. 10, there is diagrammatically illustrated atypical fiber optical instrument wherein an eye lens 53- is supportedadjacent one end face 52 of the fiber optical device and an objectivelens or the like 54 is supported adjacent the opposite end face 51thereof. The fiber optical device of FIG. 9, however, has many otherknown uses and may be placed in a catheter, for example, and used as anoptical probe for examining body fluids or it may be used as an endoiiiscope, gastroscope or as a vital sighting devices.

It is pointed out that by compacting the fibers 20 during the fusingope-ration discussed above so as to ultimately provide end faces 51 and52 which are continuous, that is, without spaces therebetween, it ispossible to produce an exceptionally high quality of optical finish onsaid faces. Porous surfaces or surfaces having interstices generallycannot be provided with the best optical polishes.

Heretofore, fiberscopes of the above general type have been subject tot1 great deal of breakage of the fibers adjacent each of the joined endsections when the fiberscopes are flexed. This is believed to be due toan abrupt transition between the rigid end sections of the fibers andthe flexible mid-sections.

In the devices formed in accordance with the invention, a gradualtransition between the rigid end portions and the flexible mid-sectionis provided to prevent undue breakage of fibers. This gradual transitionis believed to result in part from the use of the bevels 35a and 38a onthe respective support and cover parts 33 and 37 and from use of thedescribed temperature gradients in fusing of the fibers.

While, in the devices of the invention, breakage of the fibers adjacentthe rigid end sections is greatly reduced, it has been found that a moredurable final product can be had by impregnating a relatively shortsection of the disconnected portions of the fibers near the solidlyfused ends of the devices with a filler such as polyvinyl alcohol,cellulose nitrate or a suitable resin or the like. The filler Whilelending support to the fibers should be resilient enough to permit somerelative movement between the fibers.

A completely surrounding outer sheath or covering 52o (see FIG. 10) isusually applied to the device to further protect the unfused section ofthe fibers and to provide additional support at the junction of thefused and unfused section thereof.

In FIGS. 11, 12 and 13, there is shown a modification of the inventionwherein compressing forces on a stack of fiber hoops such as discussedhereinabove are applied sub stantially equally in both the vertical andhorizontal meridians thereof during a fusing operation to provide thefibers with a substantially square cross-section such as shown in FIGS.12 and 13 while simultaneously providing the said end sections withsurrounding integrally fused collars or adaptors to which auxiliary.lens systems such as shown in FIG. 10 or the like may be attached.

In forming the fused section of a stacked bundle of fiber hoops inaccordance with the modification shown in FIGS. 1113, there is provideda support 33' and cover member 37 similar to the above-described support33 and cover 3'7 arrangement. The process described hereinabove withrelation to FIGS. l-9 is followed with the exception that block-likepieces 55 preferably formed of a material similar to that of the core ofthe fibers 20 are placed at the inner sides of the refractory blocks 36which are similar to blocks 36. Pieces 55 are positioned above and belowthe bundle of fibers 263 to be fused (see FIG. 11) and the dependingsection 33' of the cover 37' is constructed to be of a widthsubstantially equal to the spacing between the refractory blocks 36' soas to engage the uppermost ends of the pieces 55.

The pieces 55 and 56 are preferably formed of a material which ischaracterized in that it has substantially the same coefiicient ofexpansion and a slightly lower melting temperature than the core of thefibers 20' and will fuse to the fibers 2% at substantially the sametemperature as is required to fuse the claddings of the fibers. Forexample, if the fibers 20 have a core of flint glass of a particularindex of refraction, the pieces 55 and 56 would be constructed of thesame or similar type of flint glass so as to be free to deform attemperatures approximately equal to or slightly below that the of thefiber.

Since the pieces 55 extend from the block 35 to the part of a widevariety of by proper control section 38 of the cover 37 (see FIG. 11) itcan be seen that :as the section 38 is lowered into the channel 34,under pressure, with the glass pieces 55 and 56 and fibers 20'heat-softened, the endwise compressing force on the heat-softened pieces55 will cause them to displace laterally against the bundle of fibers tocompress the fibers in the horizontal direction while at the same time,the uppermost piece 56 forces the fibers 20' downwardly to compress themin the vertical direction with the result that of the sizes of thepieces 55 and 56, a square or other desired cross-sectional shape can beprovided on the fibers 20' as shown in FIG. 12.

It is pointed out that the forming of the fused section of a fiberassembly as described with relation to FIGS. 11 and 12 assures that allof the fibers 20' of the assembly thereof are formed to substantiallythe same cross-sectional shape and size. That is, the fibers adjacentthe peripheral edges of the assembly are not subjected to any shearingaction or otherwise caused to become weakened in cross-section by thedownward movement of the depending part 38 of the cover member 37'.Since the outermost fibers 20' of the assembly thereof do not engage thesides of the refractory material of the support 33 but are completelysurrounded by the glass pieces 55 and 56, there is no possibility of thefibers 20' becoming mis-shapen due to sticking or resistance to downwardmovement along the sides of the refractory blocks 36 during thecompacting and fusing operation.

After fusion, the fiber bundle along with the fused pieces 55 and 56,which now form a continuous outer collar 57 (see FIGS. 12 and 13) aroundthe fiber bundle, is lifted from the support 33, cut to form the endfaces of a fiberscope and said end faces are optically ground andpolished. The cutting, grinding and polishing operations are identicalto those described above with reference to FIGS. l-9.

With a fiber optical device formed as described with relation to FIGS.11, 12 and 13, the collar 57 may be ground or otherwise provided withany desired outer contour shape, such as shown in FIG. 13, so as toprovide means for receiving auxiliary lens elements or the like such asshown, for example, by 53 and 54 of FIG. 10.

In FIGS. 14-21, the method and apparatus provided by this invention isillustrated with reference to the formation of fiber optical faceplates.According to the invention, there is preferably provided a plurality ofmembers each embodying a number of light-conducting fibers inside-by-side relation, the members being adapted to be stacked infurther side-by-side relation for forming a faceplate. For example, asshown in FIG. 14, a mandrel 58 which need not be of the collapsible typebut which is otherwise similar to the mandrel 25 can be mounted upon aconventional lathe carriage traversing mechanism or the like (notshown), and a light-conducting fiber 20 can be wound upon the mandrel toform a closely-wound helix 59, the convolutions of the helix beingsecured together throughout their length so that strips of the helix canbe cut therefrom to form flat fiber ribbons 60 as shown in FIG. 15. Forexample, the mandrel 58 can be covered with a thin plastic sheet (notshown) which is then coated with one or more layers of cement such ascellulose nitrate in a solvent of nitromethane. The fiber 20 can then bewound upon the mandrel to form the helix 59 and the helix can be coatedwith said cement. The helix can then be taped or otherwise secured tothe mandrel as at 61 and 62 and can be cut along lines 63 and 64 by anyconventional means, each cut being normal to the axes of the fibers andparallel to the mandrel axis. In this arrangement, a fiber ribbon 60 canbe stripped from the mandrel 58 between the helix cuts 63 and 64, theplastic fiber on the mandrel permitting easy removal of the ribbon fromthe mandrel. Alternatively, the helix can be scribed along lines 63 and64 and other lines similar thereto around the helix periphery. The helixcan then be removed and broken into ribbons 60 along said scribed lines,this latter technique not requiring taping or other securing of thehelix to the mandrel since the undercoat of cement on the fibers willassure retention of the helix configuration until the helix is removedfrom the mandrel. Since the fiber ribbon 60 will be coated on each sidewith the cellulose nitrate cement, the fiber ribbon or ribbons will lieflat and will not tend to curl up, and, since the ribbon has been cutfrom the helix normal to the fiber axes and parallel to the mandrelaxis, the edges 60.1 and 60.2 of the ribbon will be square-cut. As willbe readily understood, the axial length of the helix determines themaximum length of the ribbon 60 transversely of the ribbon fibers, andthe diameter of the helix determines the number of such ribbons whichcan be cut therefrom. Of course, the ribbons can be cut to shorterlengths if desired. It should also be understood that the ribbons 60 canbe formed in any comparable manner within the scope of this invention.

In forming the ribbons 60 into a fused fiber optical faceplate, theribbons are stacked within a channel 34" of a refractory support 33",the support channel preferably being lined with refractory filler blocks35" and 36 as shown in FIGS. 16 and 18 in a manner corresponding to thatdescribed with reference to FIGS. 4 and 5. For facilitating positioningof the ribbons in the support, the support can be disposed in tiltedposition upon a wedge 65, and a plate 66 can be temporarily cemented orotherwise attached to the support member edge for defining the end ofthe channel 34". The ribbons 60 can then be placed within the channeland can be taped into abutting relation to the plate 66. Where the fiberribbons are of the proper length transversely of the ribbon fibers, sothat the ribbons fit closely between the filler blocks 36", the ribbonswill stack in accurately superimposed relation with each other asdescribed above with reference to FIGS. 4 and 5. If desired, the ribbons60 can be stacked in said accurately superimposed relation between theseglass plates 67, as shown in FIGS. 16 and 18 and can be placed in thesupport member 33" and further aligned if necessary.

A cover 37" having a depending section 38" similar to the cover 37previously described can then be fitted over the support member 33 sothat the depending section of the cover is adapted to engage the fiberswithin the support member channel 34". The cover 37" and the support 33"are then enclosed with a ring-shaped heating element 40" similar to theheating element 48 previously described, and are disposed within a pressarrangement as described above with reference to FIGS. 4 and 5. Asindicated particularly in FIG. 19, the press arrangement can againprovide for heating and insulating a peripheral strip around therefractory members 33" and 37" so that the ratio of insulated surfacesof the refractory members relative to the uninsulated surfaces of themembers and to the uninsulated ends of the fiber ribbons 60 can be againadapted to establish a temperature gradient in the fibers held withinthe support, the temperature gradient being such that the fibers arebrought to fusing temperature throughout their length but are heated tothe highest temperature in a plane extending transversely of the fibersthrough the center of said support channel 34". As shown in FIG. 19, thedepending cover section 38" is preferably bevelled or otherwise flaredas at 38a" so that the cover can be pressed against the fiber ribbonswithin the support to establish a pressure gradient therein, whereby thefibers are first forced into fused relation with each other in a planeextending through the center of the section and are then forced intofused relation progressively outward from said plane, thereby to sweepair and other gases from between the fiber lengths embodied in theribbons 60. To achieve this result with fibers of relatively smalldiameter, the flare at the end of the cover section away from the fibersto be engaged need be only about 0.010 inch, the extent of this flarebeing exaggerated in FIG. 19 for clarity of illustration. If desired,the filler block 35" can also be provided with similar bevels 35a", asshown, for aiding in the establishment of said pressure gradient.

Alternatively, the support 33" can be filled with multifiber units 68each embodying a plurality of light-conducting fibers similar to thefiber 20 which have been preliminarily fused together in well-knownmanner. As will be understood, the multifiber units can be stackedWithin the support member channel 34" in side-by-side relation and canbe compacted and fused in the same manner as described immediatelyabove.

In either of these arrangements, there is formed a fiber opticalfaceplate 69 as shown in FIGS. 20 and 21 wherein the fibers embodiedtherein are compacted into intimately fused vacuum-tight relationWithout entrapment of bubbles and the like between the fibers. Further,the ends of the fibers are compacted into identical geometrical patternswherein the fibers may be altered in cross-sectional shape foreliminating interstices therebetween but retain substantially theiroriginal cross-sectional area, the fibers having their minimumcross-sectional area in a plane extending transversely through thecenter of the fibers. As will be understood, the end faces 69.1 and 69.2of the faceplate can be optically finished in conventional manner forrendering the fibers embodied therein readily receptive to light.

From the foregoing, it can be seen that simple, efiicient and economicalmeans and method have been provided for accomplishing all of the objectsand advantages of the invention. Nevertheless, it should be apparentthat many changes in the details of construction, arrangement of partsor steps in the process may be made without departing from the spirit ofthe invention as expressed in the accompanying claims and the inventionis not to be limited to the exact matters shown and described as onlythe preferred matters have been given by way of illustration.

Having described my invention, I claim:

1. Apparatus for pressing and fusing together a number of glass cladlight-conducting fibers in a bundle thereof throughout a given length ofthe bundle comprising:

supporting means of refractory material having bottom 35 and cover 38members, side walls 36 and opposite open ends forming an elongatedchannel through the supporting means, at least one of said members beingslidable in said channel in directions toward and away from the othermember, said members having facing surfaces each of a length equal tothat of said channel and between which said bundle is extended forfusion with the application of heat and a compressing force tending tomove said members one toward the other;

said facing surfaces of said bottomand cover members having oppositelydisposed end portions of their respective lengths sloped gradually awayfrom each other in directions from points internally of the supportingmeans toward each of said open ends thereof so that a transversedimension of said channel is greater at the ends of said channel than atintermediate points thereof whereby fibers in said length of said bundlewill become compacted to a greatest amount intermediately of theirextension in said channel and in progressively lesser amounts awaytherefrom upon application of said heat and compressive force.

2. The apparatus according to claim 1 further comprising heating meansencircling said supporting means intermediately of said channel therein,said heating means encompassing a relatively short portion of saidlength of said channel whereby said heat is applied to said bundle offibers with greatest intensity in an intermediate section of theextension thereof in said channel and in progressively lesserintensities away from said intermediate section.

3. The apparatus according to claim 1 further comprising channel linerpieces of glass disposed along said sides and facing surfaces of saidbottom and cover mernbers, said pieces being preselected to have afusing temperature so related to the fusing temperature of the claddingglass of said fibers in said bundle that, with said application of heatand compressing force, plastic flow of said pieces will effectcompaction of said bundle in both vertical and horizontal directionstransaxially thereof.

References Cited UNITED STATES PATENTS 2,151,874 3/1939 Simons 2,215,2149/1940 Galey 6518 X 2,354,931 8/1944 Tolman.

2,440,187 4/ 1948 Silverberg.

2,992,516 7/1961 Norton.

2,302,664 12/ 1942 Smith 65-319 XR 1,857,540 5/1932 Hardenbel'g -653 19XR 2,410,616 11/1946 Webb 65 3,196,738 7/1965 Hicks 65-4 S. LEONBASHORE, Primary Examiner. FRANK W. MIGA, Examiner.

